Math Problem Statement

In R3 you are given the vectors

a=(−4,3,−10) , and b=(−36,−5,−13) . If q=(152,46,x) belongs to span{a,b} , then what is x ?

Answer:

x

Solution

To determine xx in the vector q=(152,46,x)q = (152, 46, x) that belongs to the span of a=(4,3,10)a = (-4, 3, -10) and b=(36,5,13)b = (-36, -5, -13), we express qq as a linear combination of aa and bb:

q=αa+βbq = \alpha a + \beta b

where α\alpha and β\beta are scalars, and q=(152,46,x)q = (152, 46, x). This means we need to solve for α\alpha and β\beta in the system of equations:

(152,46,x)=α(4,3,10)+β(36,5,13)(152, 46, x) = \alpha(-4, 3, -10) + \beta(-36, -5, -13)

This yields the following system of three equations:

  1. 152=α(4)+β(36)152 = \alpha(-4) + \beta(-36)
  2. 46=α(3)+β(5)46 = \alpha(3) + \beta(-5)
  3. x=α(10)+β(13)x = \alpha(-10) + \beta(-13)

Now we can solve these equations.

Step 1: Solve for α\alpha and β\beta from the first two equations.

From the first equation:

152=4α36β152 = -4\alpha - 36\beta 4α+36β=1524\alpha + 36\beta = -152 Divide by 4: α+9β=38(Equation 1)\alpha + 9\beta = -38 \quad \text{(Equation 1)}

From the second equation:

46=3α5β46 = 3\alpha - 5\beta 3α5β=46(Equation 2)3\alpha - 5\beta = 46 \quad \text{(Equation 2)}

Step 2: Solve the system of equations.

Substituting Equation 1 into Equation 2:

From Equation 1: α=389β\alpha = -38 - 9\beta.

Substitute this into Equation 2:

3(389β)5β=463(-38 - 9\beta) - 5\beta = 46 11427β5β=46-114 - 27\beta - 5\beta = 46 11432β=46-114 - 32\beta = 46 32β=46+114-32\beta = 46 + 114 32β=160-32\beta = 160 β=5\beta = -5

Solve for α\alpha:

Substitute β=5\beta = -5 back into Equation 1:

α+9(5)=38\alpha + 9(-5) = -38 α45=38\alpha - 45 = -38 α=7\alpha = 7

Step 3: Solve for xx.

Now substitute α=7\alpha = 7 and β=5\beta = -5 into the third equation:

x=α(10)+β(13)x = \alpha(-10) + \beta(-13) x=7(10)+(5)(13)x = 7(-10) + (-5)(-13) x=70+65x = -70 + 65 x=5x = -5

Thus, the value of xx is 5\boxed{-5}.


Would you like a more detailed explanation of any step? Or do you have further questions?

Related questions:

  1. How can I find the span of two vectors in R3\mathbb{R}^3?
  2. What are the properties of linear combinations in vector spaces?
  3. How do I solve systems of linear equations using substitution or elimination?
  4. What is the concept of vector projection and how does it relate to spans?
  5. Can vectors in R3\mathbb{R}^3 ever be linearly independent or dependent?

Tip: When solving systems of linear equations, remember that you can always use matrix methods (like Gaussian elimination) to find solutions efficiently!

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Math Problem Analysis

Mathematical Concepts

Linear Algebra
Vector Spaces
Linear Combination
Systems of Equations

Formulas

q = αa + βb
4α + 36β = -152
3α - 5β = 46
x = α(-10) + β(-13)

Theorems

Span of vectors
Linear combination
System of linear equations

Suitable Grade Level

Grades 9-12